The present invention relates to an improved process for the production of conversion layers continuously on a continuously moving band or sheet-like metal surfaces of aluminum, zinc or iron by the application of a chromating solution or acid solution free of chromic acid and containing fluorides and/or compounds of titanium, zirconium or manganese, by the stationary spray method, where the solution is applied through a two-component jet spray nozzle with the aid of an inert compressed gas.
The producing of conversion layers by the spray method is known as such. For example, Ries reports, in "Metalloberflache--Angewandte Elektrochemie," 25, pages 1-6, 53-56, 75-80, 132-134, 153-159 (1971), a summary of process technology and processes for the producing of conversion layers on metal bands, and discusses also in this connection the respective spray methods. In the conventional spray methods, the respective treatment solution is sprayed on both sides of the cleaned and degreased metal band or a metal tablet with a jet system, while the spray pressure needed for this process is produced and controlled by a suitable pump. In general, spray pressures of about 0.7 to 1.5 bar over atmospheric pressure are used; however, the pressure can be increased to values of 10 to 100 bar for special high-pressure spray methods.
Common to all of these methods is the fact that they require complex pumping systems made of materials resistant to chemicals, which, on the one hand, can resist the aggressive ingredients of the treatment solutions and, on the other, guarantee a constant but controllable spray pressure. Added to this is the fact that usually relatively large volumes of liquid are sprayed on per square meter of metal surface by the known methods, which necessitate the rinsing or squeezing off of excess treatment solution after the completed reaction.